It is known that impact devices, such as demolition hammers powered by electric motors, incorporate resilient means for coupling motion of a reciprocating body into impacting motion of a ram. In my copending application, Ser. No. 534,626, it is disclosed that all known or cited prior art references utilizing some type of piston-cylinder coupler for such resilient means, incorporate air cushions or other air spring arrangements which have highly non-linear forcedisplacement spring characteristics. Such non-linearities generate wasteful extraneous harmonic vibrations and unnecessary heating, which cause considerable inefficiency and ineffectiveness of such air springs, as well as causing considerable wear and service problems for the impact device. Application Ser. No. 534,626 discloses an invention which tends to remove deficiencies of such prior art structures.